Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session IV
Sponsored by: TMS Structural Materials Division, TMS: Thin Films and Interfaces Committee, TMS: Advanced Characterization, Testing, and Simulation Committee
Program Organizers: Saurabh Puri, VulcanForms Inc; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, Korea Advanced Institute of Science and Technology; Jagannathan Rajagopalan, Arizona State University; Josh Kacher, Georgia Institute of Technology; Minh-Son Pham, Imperial College London; Robert Wheeler, Microtesting Solutions LLC; Shailendra Joshi, University of Houston
Tuesday 2:00 PM
March 16, 2021
Room: RM 17
Location: TMS2021 Virtual
Session Chair: Amit Pandey, Lockheed Martin Space
2:00 PM
Quantifying the Long-range Stress ahead of the Tip of a Dislocation Pileup at a Grain Boundary and Its Contribution to the Subsequent Structure Changes in Ti-alloys from the Atomistic to the Mesoscale: Liming Xiong1; 1Iowa State University
During the interaction between a queue of dislocations and grain boundaries (GBs) in materials, a dislocation pileup usually forms, which in turn, significantly modifies the local stress state. This process is multiscale in nature since both the atomistic GB structure and the long-range stress induced by the dislocation accumulation near the GB come into play in the subsequent structure change. Taking the Ti-alloy as a model material, here we present a concurrent atomistic-continuum method for (i) measuring not only the local Cauchy stress but also the couple stress ahead of a long-range dislocation pileup; and (ii) determining their roles in the subsequent structure change, such as phase transformation, twinning, and fracture, caused by the dislocation-GB reaction. Our results elucidate the discrepancies between fully atomistic simulations and experimental observations of dislocation-GB reactions, and highlight the importance of directly modeling dislocation-GB interactions using concurrent multiscale approaches.
2:20 PM
Dislocation Pileup Induced Transmission across Grain Boundaries in Aluminum via Molecular Dynamics Simulations: Royce Reyes1; Douglas Spearot1; 1University of Florida
The Lee-Robertson-Birnbaum criterion, the most common criterion for predicting the slip system of a transmitted dislocation, employs slip trace orientation, residual Burgers vector, and resolved shear stress. The general reliability of this criterion has been supported by experiment and simulation. However, existing simulations examine transmission due to the interaction of a grain boundary with a single dislocation, while in reality transmission is often due to the interaction of a grain boundary with a pileup of dislocations. The present work develops an atomistic simulation algorithm for creating shear dislocation loops sequentially and driving the loops toward a grain boundary, creating a dislocation pileup and ultimately inducing transmission. The algorithm is applied to a low angle Σ257 grain boundary and a high angle Σ185 grain boundary in aluminum to investigate the role of the number of dislocation loops in the pileup, magnitude of resolved shear stress, and choice of incoming slip system.
2:40 PM
Decoupling the Effect of Nanoscale Geometry and Internal Microstructure on the Mechanics of Nanoporous Pt: Ankit Gupta1; Timothy Ibru2; Antonia Antoniou2; Garritt Tucker1; 1Colorado School Of Mines; 2Georgia Institute of Technology
Nanoporous (NP) metals present added behavioral complexity arising from nanoscale. Existing scaling laws prove insufficient in explaining their mechanical behavior. In this study, the mechanical response of NP Pt is investigated through a combined computational/experimental effort unraveling the role of nanoscale geometry and internal microstructure. Atomistic NP Pt structures are first created. Internal microstructures of these structures are varied from nanocrystalline to a single-crystal without affecting the geometry. In order to separate nanoscale effects, the atomistic NP structures are scaled and printed in polymer using the SLS 3D printing technique at macro level. Macroscale porous structures with random foam geometry, but same polymer material, are also 3D printed and mechanically tested. The scaling laws of mechanical properties of porous materials are studied as function of density while individually varying their internal microstructure and geometry. The findings are explained in terms of strain accommodation in junctions, ligaments and nanoscale deformation mechanisms.
3:00 PM
Constitutive Model Materials Parameter Determination Using Cyclic Tension-compression Test Data: Dilip Banerjee1; William Luecke1; Mark Iadicola1; Evan Rust1; 1National Institute of Standards and Technology
Springback is a major problem in sheet metal forming especially for advanced lightweighting materials. Finite element (FE) simulations are conducted to understand the deformation behavior and springback in formed materials. Yoshida-Uemori (Y-U) developed a combined isotropic/kinematic hardening model that shows good capability in describing the elastic recovery and the overall tension-compression behavior. This model is described by a few parameters that are derived from test data. This paper describes a novel test setup for conducting controlled uniaxial tension/compression tests and a practical approach for determination of these parameters from tests conducted on DP steels and aluminum alloys. Optimum parameter values are obtained by conducting parameter optimization using a FE model comprising material models that include initial parameter values, where the objective function is the minimization of differences between predicted and measured stress-strain responses. Influence of these parameters on the overall deformation behavior and interdependence/correlation among the parameters are also discussed.
3:20 PM
Multiphysics Modeling of Coupled Chemical-Thermal-mechanical Phenomena in Chemically Blown Polyurethane Foams during Manufacturing: Kevin Long1; Judith Brown1; Rekha Rao1; Christine Roberts1; 1Sandia National Laboratories
PMDI (polymeric methylene diphenyl diisocyanate or polyurethane) foams encapsulate and protect fragile components. Complex chemical and physical processes occur during their manufacturing and service, however, that can cause undesired warpage. The ability to model these processes and predict resulting warpage is essential for production of parts with tight dimensional tolerances. We present our multi-physics model that describes the foam manufacturing process and predicts the post-manufactured residual stresses and warpage. The model involves four coupled conservation equations: energy (temperature field), momentum (foam velocity field), water concentration (blowing reaction), and polyol concentration (extent of polymerization), that are implemented in a loosely coupled finite element framework. Predicted deformations are compared with experimental measurements on foam parts during manufacturing. Results favorably predict temperature variation throughout the part, density variation, and warpage immediately following de-molding. This model complements our companion talk on long-term simulations of physical and chemical aging induced warpage in polyurethane foams.
3:40 PM
Effects of Phase Purity and Pore-reinforcement on the Mechanical Behavior of Metal–organic Frameworks: Kevin Schmalbach1; Zhao Wang1; Rebecca Combs1; Youxing Chen2; R. Lee Penn1; Andreas Stein1; Nathan Mara1; 1University of Minnesota; 2University of North Carolina at Charlotte
Metal-organic frameworks (MOFs) are a diverse class of materials that have proven useful for a wide range of applications including catalysis, gas storage, and absorption. Typical processing steps for MOFs are pelletization and extrusion. Thus, the mechanical behaviors of these materials are an important consideration but are rather unexplored. Here we consider the mechanical behaviors of the zirconium-based MOF NU-1000. Single crystal MOF particles were compressed in situ, and the experimental load-displacement response was used in conjunction with finite element modeling to determine the effects of phase purity and pore reinforcement on the measured elastic modulus and yield stress. The particles with an impurity phase displayed elastic moduli and yield stresses nearly an order of magnitude lower than their phase-pure counterparts. In contrast, the pore reinforcement showed no clear effect on the elastic modulus but increased the failure load by greater than 50%.